Sound reproducing apparatus



March 2 1940. v

H. E. MODQNALD 2,194,664 SOUND REPRODUCING APPARATUS Filed Feb: 17, 19382 Sheets-Sheet i March 26, 1940. H. E. McDONALD 2,194,664

SOUND REPRODUCING APPARATUS Filed Feb. 17, 1938 2 Sheets-Sheet 2Patented Mar. 26, 1940 UNITED STATES SOUND REPRODUCING APPARATUS HenryEdwin McDonald, Milsons Point, near Sydney, New South Wales, AustraliaApplication February 17, 1938, Serial No. 191,072 In Australia February18, 1937 1 Claim.

This invention has particular reference to improvements in apparatus forreproducing musical sounds and is applicable to thermionic amplifiers ofradio receiving apparatus.

An object of the present invention is to provide a reproducer wherebythe quality of the sound produced is clear and correct with respect totone.

The reproducer which is the subject matter of the invention consists ofa plurality of dynamic speakers of different capacities andcharacteristics operated in a known manner from a thermionic amplifierand disposed in a common sound chamber whose cross section increasesfrom its base towards its centre or mid-height and then reduces in crosssection towards its pper or outlet end thereof.

This sound chamber is positioned within the cabinet of the apparatuswith spaced relation in regard to one of the dynamic speakers.

In this regard the base of the sound chamber has an opening whichcoincides with an opening formed in a baille board disposed in spacedrelation to the base, said baflle board being disposed above thediaphragm of the lower of the dynamic speakers. The base of the soundchamber consists of a board which is of greater area than the baffleboard and acts as a second bafile board.

The sound chamber of the dynamic speaker assembly containing theplurality of dynamic speakers is so formed that the sound therefrom isprojected upwardly to the trumpet or horn shaped baffle. The chamber ispreferably polygonal in shape at the centre and may consist of twotapered members one of which is inverted. The chamber itself is fittedinternally with V-shaped fillers between the respective speakers to formsound directors and internal baflies.

In order that the invention may be more readily understood referencewill now be made to the accompanying drawings, wherein- Figure 1 is anelevational View of the dynamic speaker assembly.

Figure 2 is a sectional plan view of the sound chamber on the line 6-5of Figure 1 showing the internal structure.

Figure 3 is a detail view of portion of the absorber casing which isdisposed around the sound chamber of the speaker assembly seen in brokenlines in Figure 1.

Figure 4 is a sectional elevation showing the large trumpet.

Figure 5 is an end elevation of the trumpet.

The dynamic speaker assembly 33 is disposed adjacent the soundreproducing apparatus and includes a plurality of tone compartmentswherein treble and medium and bass tones are produced by respectivespeakers as will be explained later.

The dynamic speaker assembly 33, Figure 1, is mounted upon a base 34which acts as a bailie board and has a baffie board 35 suspendedtherefrom.

The base or baffle 34 and the bafile board 35 are provided with openings36 and 3'! respectively, said openings being concentric. The opening 36in the base 34 being of larger diameter than the opening 31 in thebaffle board 35. The opening 31 in the bafile board 35 is covered 5 withgauze 35 and has the bass dynamic speaker 38 disposed thereunder as seenin Figure 1.

An air gap 40 is provided between the base or baffle 34 and the baffleboard 35.

The sound chamber being the internal portion of the dynamic speakerassembly 33, is disposed above the base 34 and is preferably ofpolygonal shape at the centre, being formed preferably of two hollowtapered members 4 l42 united at their base 43, the respective narrowedportions forming the top 44 and the bottom 45 respectively of thechamber.

As illustrated the sound chamber is octagonal at the centre line 43 andhas eight faces above and an equal number below the centre line 43. Fourof the lower faces are provided with orifices 4B, 41, 48 and 49 overwhich dynamic speakers 50 for use with varying frequencies are secured,With the object of producing combined sounds of desired degrees, whichharmonize with the sound produced by the dynamic speaker 39 suspended tothe bafile board 35.

The respective dynamic speakers 50 and 39 are controlled from a switchpanel 5| which is disposed outside the casing.

The sound chamber is divided into a plurality of tone spaces 52 byfillers 53 which act not only as sound directors but also preventclashing and humming caused by dead air in unfilled spaces.

A space or air gap 54 is left between the base of the horn 55 and thetop of the sound chamber space. The space or air gap acts with the aircushion formed by air pressure produced by the sharply slanting roof ina give and take move- 50 ment of the air cushion, thus accentuating loudor modifying soft sounds from double forte to pianissimo.

A housing is provided to surround the dynamic speaker assembly 33 asshown in broken lines in Figure 1 and this is composed of zig-zagabsorbing material 56 spaced apart as seen in Figure 3. This material 56acts as an external absorbing lining for the dynamic speaker assembly33,

The trumpet or horn shaped baffle 55 shown in Fig. 1 may take the formshown generally at 6| in Figs. 4 and 5. These horn shaped baffles may besupported above the sound cham ber by means of a member El having an arm60 carrying a ring engaging the lower end of the trumpet. The trumpet orhorn shaped bafile illustrated in Figs. 4 and 5 has a plurality of soundreflecting surfaces 62, 83, 64, 65 and 66.

I claim:

Sound reproducing apparatus comprising, a

hollow casing of polygonal shape in a central transverse section andtapering inwardly towards each end to provide a sound chamber, a baffleboard engaging one end of the casing and supporting said casing, asecond baffle board secured to the first bafl'le board and spacedtherefrom, a horn-shaped baflie mounted on the other end of the casingcommunicating with the sound chamber, said horn-shaped baflle having aplurality of sound reflecting faces, each baflle board having an openingtherein, a dynamic speaker mounted on the second baffle board adjacentthe opening therein, said casing having orifices therein, and dynamicspeakers mounted on the casing adjacent said orifices.

HENRY EDWIN MCDONALD.

